1. Field of the Invention
The present invention relates to nanometric or mesoscopic dissymmetric particles comprising a part consisting of an inorganic material and a part consisting of an organic material, and also to a method for preparing them.
2. Description of the Related Art
It is known practice to prepare dissymmetric particles comprising two organic parts by reaction of latex particles (polystyrene) with styrene monomer in the presence of divinylbenzene as a crosslinking reagent, 2,2′-azobis(2-methylbutyronitrile) as a polymerization initiator and poly-N-vinylpyrrolidone as a stabilizer. Such a method thus consists in bringing about the growth of a polymer by a free-radical process using a particle of latex that has been preconstituted and swollen with a mixture of monomers under conditions such that phase-separation of the latex and of the polymer formed is promoted [cf. H. R. Sheu, et al., J. of Polymer Science: Part A: Polymer Chemistry, Vol. 28, 653-667 (1990)].
The preparation of solid particles that are amphiphilic in nature is known from WO 01/85324. The method consists in partially modifying the surface of a mineral particle with organic chains which are hydrophobic in nature. The product obtained is an emulsifying composition comprising nanometric mineral particles that have a core made of mineral material and a hydrophobic organic coating on part of its surface, the hydrophobic coating being obtained in particular by covalent bonding using a compound comprising a long alkyl chain and a silanol group.
A method for preparing silica particles, at the surface of which small polystyrene particles are attached, is also known. Said method comprises a first step during which a suspension of silica particles is prepared, a second step during which a hydrophilic PEG methacrylate macromonomer is adsorbed onto said silica particles, and a third step during which emulsion polymerization of styrene is carried out in the presence of the modified silica particles. The concentrations of macromonomer used are 0.1 and 0.05 g.l−1 for a concentration of silica particles of 10 g.l−1. The particles obtained by means of this method consist of a silica core and of small nodules of polymer distributed evenly at the surface of the silica core (cf. Syntheses of Raspberrylike Silica/Polystyrene Materials, S. Reculusa, et al., Chem. Mater. 2002, 14 2354-2359 (published on Apr. 27, 2002)).